Hi I've been lurking here for a while and decided it's time to register on this vast board. I've been toying a bit with diy and decided I want to build a cmos synth. I love the simplicity of cmos synths and I'm not really interested in 1V/Oct tracking, just want to make some cool sounds to sample.

Excuse the noob level, but I have read Stanley Lunetta's method of wiring up chips directly from the pins to banana jacks. Does a connection also need to be taken to ground from the jack? I read you must run to ground any unused pins so I wondered if you must also ground the jack for when a connection is not made?

Does a connection also need to be taken to ground from the jack? I read you must run to ground any unused pins so I wondered if you must also ground the jack for when a connection is not made?

If I understand your question correctly, then yes. If you connect a jack to a pin but don't plug anything in then you want it to be grounded. This is
usually done with a pulldown resistor between the input pin and GND (somewhere between 10K ... 1M). For some inputs however you might want
a pullup resistor (connected to V+ instead of GND) depending on it's function._________________"My perf, it's full of holes!"http://phobos.000space.com/http://www.acidtrash.com/Stickney Synthyards

This is usually done with a pulldown resistor between the input pin and GND (somewhere between 10K ... 1M). For some inputs however you might want
a pullup resistor (connected to V+ instead of GND) depending on it's function.

Thanks, but to be honest I am totally in the dark about wiring up jacks. There is lots of info and schematics online for beginners but not really much info on how you integrate jacks into the circuit. Could you explain what you mean using the schematic below (thanks to beavis audio).

The obvious connection to me in this schmatic is the output. No need to ground this. But how to hook up a jack to the input is where I get lost. Thanks for your time and patience.

I've just been checking out some of your schematics and I think I understand what you mean. In your schematic below I can see you have a Filter CV input with a 100k resistor to ground. Off this goes the connection to the input. I think this is what you meant?

The obvious connection to me in this schmatic is the output. No need to ground this. But how to hook up a jack to the input is where I get lost. Thanks for your time and patience.

well that circuit doesn't have an input allthough you could add one but you wouldn't need a pulldown resistor. In my VCF circuit the function
of the potentiometer at the input is to control the CV level, but if you don't connect anything it does indeed also function as a pulldown resistor.
But I drew a better example.

it's an oscillator that is similar to the one from Beavis Audio buth made with a schmitt trigger NAND gate instead of an inverter. It will only
oscillate when the input pin is high which makes it possible to turn it on/off. You can do this with a switch but you can also control it with
another oscillator or some more complex logic.

There are two options:
1 - use a pulldown resistor. If you don't connect anything to the input the oscillator will be off. A high signal (+) will turn it on.
2 - use a pullup resistor. If you don't connect anything to the input the oscillator will be on. A low signal (GND) will turn it off.

So depending on what the function of the input pin is you can either use a pulldown or pullup resistor. a high value (1M) will make it sensitve to
noise while a low value (10K) will draw more current.

The pull down resistors are placed on the input pins to make the chip more reliable/less chaotic. Sometimes you do use a pull up resistor on some ics because that particular pin (like the strobe and output enable pins of a 4094 shift register) have to be "High" for the chip to do it "thing".

As for jacks:
Generally speaking, you build your 40106 oscillators without any jacks on the inputs; that's possible with the 4093 as phobos demonstrated. The 40106 oscillators are self running if you will, only needing a jack on the output to send the signal on to the inputs of other chips or just to be mixed with other oscillators.

Regarding grounding the jacks: I have used nuts and bolts as my connectors in the past and they only had one wire (either coming from the input pin or output pin of a chip). I wire up the banana jacks the same way with no issues.

Smoothing out the oscillator: a simple passive low pass filter can do that (I believe fluxmonkey's site has a swell write up on that). The best place to think about smoothing the audio is at the tail end of the circuit; in lunetta practices, when the patching is done. Rounding the square wave too much with a filter and then using it as a clock source can be tricky on chips looking for a nice strong, square signal.

As for jacks:
Generally speaking, you build your 40106 oscillators without any jacks on the inputs; that's possible with the 4093 as phobos demonstrated. The 40106 oscillators are self running if you will, only needing a jack on the output to send the signal on to the inputs of other chips or just to be mixed with other oscillators.

That has really cleared up a lot regarding the inputs of the 40106 and other chips. Thanks!

Draal wrote:

Regarding grounding the jacks: I have used nuts and bolts as my connectors in the past and they only had one wire (either coming from the input pin or output pin of a chip). I wire up the banana jacks the same way with no issues.

So basically there is no grounding here whatsoever. Great!
Have you grounded yourself after that extra cup of java? hehe

One last question i have is regarding amplitude modulation in digital circuits. Basically... is difficult to modulate the amplitude of the audio signal, like for example, a traditional ADSR or LFO applied to a VCA? Or put another way - how can you modulate the amplitude in a cmos synth?

I am sufficiently "java full" now . The only grounds I'm concerned with are pins 7 or 8 on most of the cmos chips. As long as I make sure they all go to a common point (in may case, a piece of strip board that has a long row for all my 9v signals and a separate row just for all my ground connections), I know my lunette modules work.

As far as amplitude modulation, vca's and the sort, they unfortunately are out of my area of expertise. I tried a few experiments/layouts but they usually left me disappointed. Grand Pooba Mosc mentioned a long time ago in a thread far far away that those types of circuits may not work the same way as we see in real modulars.

That said, I'm sure there are guys on here with some strategies that may work well for you ._________________Zontar Prevails!

One last question i have is regarding amplitude modulation in digital circuits. Basically... is difficult to modulate the amplitude of the audio signal, like for example, a traditional ADSR or LFO applied to a VCA? Or put another way - how can you modulate the amplitude in a cmos synth?

Hi. I'm sure that PHOBoS can give you far more details on this than I can, but two possibilities come to mind. One is to use a transistor VCA as PHOBoS does here (near the bottom of the 2nd page):

Here you are also shown how to make a home made vactrol (in case you have no idea what I'm talking about ). One example uses purely passive components and the other op-amps, but transistor amps could be subtituted. I've not tried the vactrol idea yet, but it should work. I know that PHOBoS' transistor VCAs do work though.

Here you are also shown how to make a home made vactrol (in case you have no idea what I'm talking about ). One example uses purely passive components and the other op-amps, but transistor amps could be subtituted. I've not tried the vactrol idea yet, but it should work. I know that PHOBoS' transistor VCAs do work though.

Gary

Thanks a lot for the great links and info. Plenty more more reading up to do! (maybe java coffee will help) This diy world is a very big rabbit hole. I don't think Alice would have survived if she fell into the synth diy rabbit hole! hehe

I am appreciating the tone on this board. Everyone is very welcoming and tolerant to a fellow noob!

Phobos' 555 envelope generator and transistor based vca is genius. It's great you can build a simple envelope generator and vca without needing a bipolar supply.

When I think how much I paid for an Oakley envelope generator and seperate vca (when I had cash) that 555 inspired circuit is brilliant. With 1 chip and a hand full of components amplitude modulation is on! cheers

Thanks a lot for the great links and info. Plenty more more reading up to do! (maybe java coffee will help) This diy world is a very big rabbit hole. I don't think Alice would have survived if she fell into the synth diy rabbit hole! hehe

I am appreciating the tone on this board. Everyone is very welcoming and tolerant to a fellow noob!

No problem - PHOBoS et al. did all of the work really . Yes, you really have opened a big can of worms by visiting this site (to change the metaphor). It is really, seriously addictive - you have been warned!

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